Reduced blend artifacts in a multiple digital projector system

ABSTRACT

Techniques for reducing blend artifacts in a multiple digital projector system are provided, including a first and second projector, having respective projection fields which overlap in a blend zone and one or more control devices configured to: for a given pixel of a common image frame projected by both the first projector and the second projector in the blend zone, the given pixel of the common image frame comprising a plurality of bitplanes arranged in a sequence, control the first projector to project a first portion of the plurality of bitplanes according to the sequence; and control the second projector to project a second portion of the plurality of bitplanes according to the sequence, the second portion complementary to the first portion, such that in the common image frame only one of the first projector and the second projector projects any given bitplane of the plurality of bitplanes.

FIELD

The specification relates generally to projectors, and specifically toreducing blend artifacts in a multiple digital projector system.

BACKGROUND

When images from multiple digital projectors are overlapped, images maynot appear uniform because the brightness in the overlap, referred to asa blend zone, is higher than that in the areas where only one projectoris forming the image. The overlap is referred to as a blend zone as theimages from each of the projectors are blended together in the blendzone. Image brightness in blend zones is often managed through acombination of electronic and optical blending. In optical blendingoptical elements (such as filters) are used to adjust the brightness ofeach image. In electronic blending, the brightness of each image isadjusted so that when overlapped a constant brightness is presented tothe viewer across the overlap region. Unfortunately, with electronicblending it is possible that a viewer's eyes, when moving (e.g.saccading) quickly across the blend region, see bands of brightnessand/or darkness and/or colors. These blend zone artifacts distract fromthe image and reveal the multiple projectors used to construct the finalimage.

SUMMARY

In general, this disclosure is directed to a system in which digitalprojectors are coordinated to project bitplanes in a blend zone suchthat only one projector is projecting a bitplane of a given pixel at anyone time. For example, each projector is controlled to project a commonimage frame in a blend zone, and for each given pixel of the commonimage frame, which is made up a of a plurality of bitplanes to beprojected in a sequence: each projector projects a respective portion ofthe plurality of bitplanes in the sequence such that only one of theprojectors is projecting any given bitplane of the plurality ofbitplanes at any time. In other words, bitplanes are projected in asequence that is distributed between the projectors, such that bitplanesprojected by each projector do not overlap.

In this specification, elements may be described as “configured to”perform one or more functions or “configured for” such functions. Ingeneral, an element that is configured to perform or configured forperforming a function is enabled to perform the function, or is suitablefor performing the function, or is adapted to perform the function, oris operable to perform the function, or is otherwise capable ofperforming the function.

It is understood that for the purpose of this specification, language of“at least one of X, Y, and Z” and “one or more of X, Y and Z” can beconstrued as X only, Y only, Z only, or any combination of two or moreitems X, Y, and Z (e.g., XYZ, XY, YZ, ZZ, and the like). Similar logiccan be applied for two or more items in any occurrence of “at least one. . . ” and “one or more . . . ” language.

An aspect of the specification provides a system comprising: a firstprojector and a second projector having respective projection fieldswhich overlap in a blend zone, and one or more control devicesconfigured to: for a given pixel of a common image frame projected byboth the first projector and the second projector in the blend zone, thegiven pixel of the common image frame comprising a plurality ofbitplanes arranged in a sequence, control the first projector to projecta first portion of the plurality of bitplanes according to the sequence;and control the second projector to project a second portion of theplurality of bitplanes according to the sequence, the second portioncomplementary to the first portion, such that in the common image frameonly one of the first projector and the second projector projects anygiven bitplane of the plurality of bitplanes.

The one or more control devices can comprise a first control device atthe first projector, a second control device at the second projector,and one or more system control devices in communication with the firstcontrol device and the second control device, the one or more systemcontrol devices configured to: transmit, to the first control device andthe second control device, the common image frame and associated dataindicating a respective geometry of each of the first projector and thesecond projector with respect to the blend zone, each of the firstcontrol device and the second control device configured to control arespective projector to project a respective portion of the plurality ofthe bitplanes according to the respective geometry, such that in thecommon image frame only one of the first projector and the secondprojector projects any given bitplane of the plurality of bitplanes.

Each of the first projector and the second projector can be controlledto project a respective portion of the plurality of bitplanes in thesequence according to a blend coefficient determined from associateddata indicating a respective geometry of each of the first projector andthe second projector with respect to the blend zone.

The one or more control devices can be further configured to: for eachof all pixels of the common image frame projected by both the firstprojector and the second projector in the blend zone, all the pixelsincluding the given pixel, each of the pixels of the common image framecomprising a plurality of respective bitplanes arranged in a respectivesequence: control the first projector to project a respective firstportion of the plurality of respective bitplanes according to therespective sequence; and control the second projector to project arespective second portion of the plurality of respective bitplanesaccording to the respective sequence, the respective second portioncomplementary to the respective first portion, such that for each of thepixels in the common image frame only one of the first projector and thesecond projector projects any given respective bitplane of the pluralityof respective bitplanes.

The one or more control devices can be further configured to controleach of the first projector and the second projector to interleave thefirst portion and the second portion of the plurality of bitplanesaccording to the sequence.

The one or more control devices can be further configured to ditheradjacent bitplanes for each of the first projector and the secondprojector in the blend zone.

Each of the first projector and the second projector can comprise one ormore of a digital projector, a DMD (digital multimirror projector) basedprojector and an LCOS (liquid crystal on silicon) projector operated inan on-off mode.

Each of the first projector and the second projector can be configuredto mask bitplanes that are not to be projected.

Each of the first projector and the second projector can be controlledto project a respective portion of the plurality of bitplanes in thesequence according to a round-robin.

The system can further comprise a plurality of projectors, including thefirst projector and the second projector, each having a respectiveprojection field which at least partially overlap in the blend zone, thegiven pixel of the common image frame projected by each of the pluralityof projectors in the blend zone, the given pixel of the common imageframe comprising the plurality of bitplanes arranged in the sequence,and the one or more control devices can be further configured to:control each of the plurality of projectors to project a respectiveportion of the plurality of bitplanes according to the sequence, each ofthe respective portions being complementary to all others of therespective portions, such that in the common image frame only one of theplurality of projectors projects any given bitplane of the plurality ofbitplanes.

An aspect of the specification provides a method comprising: at a systemcomprising: first projector and a second projector having respectiveprojection fields which overlap in a blend zone, and one or more controldevices, for a given pixel of a common image frame projected by both thefirst projector and the second projector in the blend zone, the givenpixel of the common image frame comprising a plurality of bitplanesarranged in a sequence, controlling, using the one or more controldevices, the first projector to project a first portion of the pluralityof bitplanes according to the sequence; and controlling, using the oneor more control devices, the second projector to project a secondportion of the plurality of bitplanes according to the sequence, thesecond portion complementary to the first portion, such that in thecommon image frame only one of the first projector and the secondprojector projects any given bitplane of the plurality of bitplanes.

The one or more control devices can comprise a first control device atthe first projector, a second control device at the second projector,and one or more system control devices in communication with the firstcontrol device and the second control device, and the method can furthercomprise: transmitting, using the one or more system control devices, tothe first control device and the second control device, the common imageframe and associated data indicating a respective geometry of each ofthe first projector and the second projector with respect to the blendzone, each of the first control device and the second control deviceconfigured to control a respective projector to project a respectiveportion of the plurality of the bitplanes according to the respectivegeometry, such that in the common image frame only one of the firstprojector and the second projector projects any given bitplane of theplurality of bitplanes.

Each of the first projector and the second projector can be controlledto project a respective portion of the plurality of bitplanes in thesequence according to a blend coefficient determined from associateddata indicating a respective geometry of each of the first projector andthe second projector with respect to the blend zone.

The method can further comprise: for each of all pixels of the commonimage frame projected by both the first projector and the secondprojector in the blend zone, all the pixels including the given pixel,each of the pixels of the common image frame comprising a plurality ofrespective bitplanes arranged in a respective sequence: controlling,using the one or more control devices, the first projector to project arespective first portion of the plurality of respective bitplanesaccording to the respective sequence; and controlling, using the one ormore control devices, the second projector to project a respectivesecond portion of the plurality of respective bitplanes according to therespective sequence, the respective second portion complementary to therespective first portion, such that for each of the pixels in the commonimage frame only one of the first projector and the second projectorprojects any given respective bitplane of the plurality of respectivebitplanes.

The method can further comprise controlling, using the one or morecontrol devices, each of the first projector and the second projector tointerleave the first portion and the second portion of the plurality ofbitplanes according to the sequence.

The method can further comprise dithering, using the one or more controldevices, adjacent bitplanes for each of the first projector and thesecond projector in the blend zone.

Each of the first projector and the second projector can be configuredto mask bitplanes that are not to be projected.

Each of the first projector and the second projector can be controlledto project a respective portion of the plurality of bitplanes in thesequence according to a round-robin.

The system further can comprise a plurality of projectors, including thefirst projector and the second projector, each having a respectiveprojection field which at least partially overlap in the blend zone, thegiven pixel of the common image frame projected by each of the pluralityof projectors in the blend zone, the given pixel of the common imageframe comprising the plurality of bitplanes arranged in the sequence,and the method can further comprise: controlling, using the one or morecontrol devices, each of the plurality of projectors to project arespective portion of the plurality of bitplanes according to thesequence, each of the respective portions being complementary to allothers of the respective portions, such that in the common image frameonly one of the plurality of projectors projects any given bitplane ofthe plurality of bitplanes.

A further aspect of the specification provides a computer-readablemedium storing a computer program, wherein execution of the computerprogram is for: at a system comprising: first projector and a secondprojector having respective projection fields which overlap in a blendzone, and one or more control devices, for a given pixel of a commonimage frame projected by both the first projector and the secondprojector in the blend zone, the given pixel of the common image framecomprising a plurality of bitplanes arranged in a sequence, controlling,using the one or more control devices, the first projector to project afirst portion of the plurality of bitplanes according to the sequence;and controlling, using the one or more control devices, the secondprojector to project a second portion of the plurality of bitplanesaccording to the sequence, the second portion complementary to the firstportion, such that in the common image frame only one of the firstprojector and the second projector projects any given bitplane of theplurality of bitplanes. The computer-readable medium can comprise anon-transitory computer-readable medium.

BRIEF DESCRIPTIONS OF THE DRAWINGS

For a better understanding of the various implementations describedherein and to show more clearly how they may be carried into effect,reference will now be made, by way of example only, to the accompanyingdrawings in which:

FIG. 1 depicts a blending scheme for blending overlapping images inblend zone according to the prior art.

FIG. 2 depicts a system for blending overlapping images according tonon-limiting implementations.

FIG. 3 depicts a block diagram of a flowchart of a method for blendingoverlapping images, according to non-limiting implementations.

FIG. 4 depicts an example of applying the method of FIG. 3 to atwo-projector system having one blend zone, according to non-limitingimplementations.

FIG. 5 depicts a scheme for implementing the method of FIG. 3 in acombination of physical and logical components, according tonon-limiting implementations.

DETAILED DESCRIPTION

Attention is first directed to FIG. 1, which depicts a blending schemeaccording to the prior art. It is assumed in FIG. 1 that a projector Aand a projector B are each projecting a respective image A, B onto asurface (e.g. a screen and the like) and images A and B overlap in ablend zone. It is further assumed that the portion of each of images A,B in the blend zone are the same, e.g. a common image, and further thatprojector A and projector B are being controlled to blend the commonimage of images A, B together in the blend zone. According to thedepicted blend scheme, the contribution from projector A decreaseslinearly (i.e. left-to-right, from pixel to pixel) in the blend zone asa function of pixel position, while the contribution from projector Bincreases linearly (i.e. left-to-right, from pixel to pixel) in theblend zone as a function of pixel position. Hence, for example, in aregion of the blend zone where projector A provides 70% of thebrightness of the common image, projector B provides 30% of thebrightness of the common image; similarly, in a region of the blend zonewhere projector A provides 50% of the brightness of the common image(e.g. about half way), projector B provides 50% of the brightness of thecommon image; and in a region of the blend zone where projector Aprovides 30% of the brightness of the common image (e.g. about halfway), projector B provides 70% of the brightness of the common image.

FIG. 1 also depicts how light is projected by each of projectors A, B ina common frame period for a given pixel in each of the 70/30, 50/50,30/70 regions: for example, the light intensity vs. time graphsgenerically show bitplanes projected by each of projector A, B for asingle pixel in each region (as well as outside the blend zone).

Specifically, in a given frame period, the portion of the common imageprojected by each of projector A and projector B are overlaid onto eachother. For example. In the region where projector A provides 70% of thebrightness, and projector B provides 30% of the brightness, projector Ais controlled to project at 100% of the brightness of the frame, but for70% of the time, and similarly, projector B is controlled to project at100% of the brightness of the frame, but for 30% of the time;furthermore, there is no coordination between when each projector isprojecting the respective portion of the frame, so that the image fromprojector A is projected simultaneously with the image from projector B.

This leads to the appearance of bright/dark/colored bands in the blendzone as the light from each projector “piles up” due to two overlappingpixels: one pixel projected by projector A at, for example, 100%intensity, for 70% of the frame period overlapping with a second pixelat 100%, for 30% of the frame period, rather than a single pixel at 100%intensity for 100% of the frame period, as occurs outside the blendzone. Whereas the 100% intensity pixel would use all bitplanes,resulting in a fixed intensity level over the frame time, the 30%intensity pixel uses some bitplanes, and the 70% intensity pixel usesmany, and/or all, of those bitplanes and some additional bitplanes. Whenoverlaid onto each other, the effective light is twice the intensityduring the 30% bitplanes, reduced to normal intensity for the 70%-onlybitplanes, and then dark for the remaining bitplanes. This can appear asa bright band during the 30% bitplanes and a dark band for the remainingbitplanes if the viewer's eye moves across the blend zone. It is furthernoted that in some situations, bitplanes can be turned on and off indifferent orders and/or the bitplanes can be reordered according to ascheme not based solely on intensity. Regardless, such bright and darkbands can still occur in these schemes.

A similar problem occurs even for the 50/50 projection region where allthe light piles up into one region, leading to one bright band that istwice the desired intensity, and dark bands on either side of the brightband. In other words, in the 50/50 projection region, each projector A,B simultaneously projects its respective portion of a pixel.

To address this problem, described herein is a blending scheme in which,instead of reducing pixel intensities within a blend region prior tobitplane selection, a time based scheme is used, where bitplanes areselected for the full pixel intensity and then bitplanes are “maskedoff” at each projector such that only one projector within a blend zoneilluminates a particular bitplane.

Thus, modifying the scheme of FIG. 1 at, for example, the 50/50projection region, both projector A and projector B can convert the 100%pixel intensity to bitplanes, but projector A turns on half of thebitplanes while projector B turns on the other half; furthermore,projection by each projector A, B is synchronized such that only one ofprojector A and projector B is projecting a bitplane for a given pixelat any given time. Similarly, for the 70/30 projection region, bothprojector A and B convert the 100% pixel intensity to bitplanes, butprojector A turns on 70% of the bitplanes while projector B turns on theremaining 30%, the two sets of bitplanes projected by each projector A,B being complimentary to each other; in other words, projection by eachprojector A, B is synchronized such that only one of projector A andprojector B is projecting a bitplane for a given pixel at any giventime. As will be described herein, such a scheme can reduce theabove-described banding, and leads a viewer to see continuous light.

Attention is next directed to FIG. 2 which depicts a system 200comprising: a first projector 201-A and a second projector 201-B havingrespective projection fields 203-A, 203-B which overlap in a blend zone205, and one or more control devices 210-A, 210-B, 210-C configured to:for a given pixel of a common image frame projected by both firstprojector 201-A and second projector 201-B in blend zone 205, the givenpixel of the common image frame comprising a plurality of bitplanesarranged in a sequence, control the first projector 201-A to project afirst portion of the plurality of bitplanes according to the sequence;and control the second projector 201-B to project a second portion ofthe plurality of bitplanes according to the sequence, the second portioncomplementary to the first portion, such that in the common image frameonly one of the first projector 201-A and second projector 201-Bprojects any given bitplane of the plurality of bitplanes. This schemewill be described in further detail below.

Furthermore, as depicted, one or more control devices 210-A, 210-B,210-C includes a first control device 210-A at first projector 201-A, asecond control device 210-B at second projector 201-B, and a systemcontrol device 210-C (including one or more system control devices) incommunication with the first control device 210-A and the second controldevice 210-B via respective communication links, which can be wired orwireless as desired. Components of each of first control device 210-Aand second control device 210-B can be integrated with and/or separatefrom, each respective projector 201-A, 201-B.

As depicted, control device 210-A comprises a memory 222-A storing anapplication 223-A and an interface 224-A; control device 210-B comprisesa memory 222-B storing an application 223-B and an interface 224-B; andcontrol device 210-C comprises a memory 222-C storing an application223-C and an interface 224-C.

For simplicity, first projector 201-A and second projector 201-B will beinterchangeably referred to hereafter, collectively, as projectors 201,and generically as a projector 201. Similarly, projection fields 203-A,203-B will be interchangeably referred to hereafter, collectively, as aprojection field 203, and generically as a projection field 203.Similarly, one or more control devices 210-A, 210-B, 210-C will beinterchangeably referred to hereafter, collectively, as control devices210, and generically as a control device 210. Similarly, memory 222-A,222-B, 222-C will be interchangeably referred to hereafter,collectively, as memory 222, and generically as a memory 222. Similarly,applications 223-A, 223-B, 223-C will be interchangeably referred tohereafter, collectively, as applications 223, and generically as anapplication 223. Similarly, interfaces 224-A, 224-B, 224-C will beinterchangeably referred to hereafter, collectively, as interfaces 224,and generically as an interface 224.

System control device 210-C can include, but is not limited to, one ormore of a content player, an image generator, and image renderer, andthe like which processes and/or “plays” and/or generates image data, forexample by producing projection data suitable for processing andprojection by each projector 201 and an associated control device 210-A,210-B. For example, such image data (not depicted) can include, but isnot limited to, one or AVI files, one or more JPG files, a PNG file, andthe like. Projection data can include, but is not limited to, HDMI data,VGA data, and/or video transport data. In other words, control device210-C can process image data to produce respective projection data whichis transmitted to each control device 210-A, 210-C, each of which, inturn, processes the respective projection data into a format suitablefor projection by a respective projector 201. In particular, asdescribed in detail below, the data transmitted to each control device210-A, 210-C is not necessarily the same, but rather is specific to eachassociated projector 201, for example to indicate a respective geometryof each projector 201. Furthermore, system 200 can further include oneor more system control devices similar to device 210-C (e.g. including aplurality of system control devices); in these implementations, eachprojector 201 can receives images from an image generator and/or systemcontrol device dedicated to that projector 201. Such implementations caninclude a host controller computing device that co-ordinates the outputof the image generators (e.g. such a host controller computing devicecan also be referred to as a system control device that controls othersystem control devices, that are each, in turn, dedicated to controllinga given projector). In other words, a wide variety of system controlarchitectures are within the scope of present implementations.

Control device 210-C can hence comprise, for example, a server and thelike, configured to generate and/or render images as image data.Alternatively, control device 210 can generate image data usingalgorithms, and the like, for generating images.

Each control device 210-A, 210-B can comprise a respective controldevice integrated with each projector 201.

Each projector 201 comprises a digital projector configured to digitallyproject images and control brightness of pixels in projected imagesusing bitplanes. While present implementations contemplate that eachprojector 201 comprises one or more of a DLP™ (digital light processing)DMD (digital multimirror device) based projector, other types ofprojection technologies that use bitplanes to control brightness arewithin the scope of present implementations. For example, one or more ofprojectors 201 can include an LCOS (Liquid Crystal on Silicon) basedprojector, and the like, but operated in an on-off mode, such that eachpixel is either “on” or “off” and a brightness of each pixel controlledusing bitplanes, similar to operation of a DMD based digital projector.

Furthermore, while only two projectors 201 are depicted, system 200 cancomprise a plurality of projectors 201 and/or three or more projectors,each configured to project respective projection data comprising, forexample, portions of a larger tiled image to be projected. Indeed, it isassumed that images projected by each projector 201 into a respectiveprojection field 203, and which overlap and are blended together inblend zone 205, together form a tiled image. Indeed, while not depicted,it is assumed that each projection field 203 intersects a surface and/orscreen such that the tiled image is projected onto the surface and/orscreen.

While not depicted, system 200 can comprise other devices, including,but not limited to, warping devices and the like, configured to warpprojection data for projection onto a three-dimensional surface.

Each control device 210, can comprise any suitable computing device,including but not limited to a graphics processing unit (GPU), agraphics processing device, a graphics processing engine, a videoprocessing device, a personal computer (PC), a server, and/or a controldevice integrated with a respective projector 201, and the like, andeach generally comprises a memory 222 and a communication interface 224(interchangeably referred to hereafter as interface 224) and optionallyany suitable combination of input devices and display devices.

Each control device 210 can further comprise a processor and/or aplurality of processors, including but not limited to one or morecentral processors (CPUs) and/or one or more processing units and/or oneor more graphic processing units (GPUs); either way, each control device210 comprises a hardware element and/or a hardware processor. Indeed, insome implementations, each control device 210 can comprise an ASIC(application-specific integrated circuit) and/or an FPGA(field-programmable gate array) specifically configured to implement thefunctionality of each control device 210. Hence, each control device 210is not necessarily a generic computing device and/or a generic processorand/or a generic component, but a device specifically configured toimplement specific functionality, as described in further detail below.For example, control devices 210, together, can specifically comprise anengine configured to reduce blend artifacts in a multiple digitalprojector system using the bitplane projection scheme described herein.

Each memory 222 can comprise a non-volatile storage unit (e.g. ErasableElectronic Programmable Read Only Memory (“EEPROM”), Flash Memory) and avolatile storage unit (e.g. random access memory (“RAM”)). Programminginstructions that implement the functional teachings of each controldevice 210 as described herein are typically maintained, persistently,in each memory 222 and used by each control device 210 which makesappropriate utilization of volatile storage during the execution of suchprogramming instructions. Those skilled in the art recognize that eachmemory 222 is an example of computer readable media that can storeprogramming instructions executable on each control device 210.Furthermore, each memory 222 is also an example of a memory unit and/ormemory module and/or a non-volatile memory.

In particular, each memory 222 stores a respective application 223,which, when processed by one or more control devices 210, enables theone or more control devices 210 to: for a given pixel of a common imageframe projected by both first projector 201-A and second projector 201-Bin blend zone 205, the given pixel of the common image frame comprisinga plurality of bitplanes arranged in a sequence, control the firstprojector 201-A to project a first portion of the plurality of bitplanesaccording to the sequence; and control the second projector 201-B toproject a second portion of the plurality of bitplanes according to thesequence, the second portion complementary to the first portion, suchthat in the common image frame only one of the first projector 201-A andsecond projector 201-B projects any given bitplane of the plurality ofbitplanes.

Furthermore, specific functionality of components of system 200 can bemaintained at respective control devices 210. For example, as describedabove, control device 210-C can further play and/or generate image datato produce projection data specific to a given projector 201, which isin turn transmitted to control devices 210-A, 210-C, each of whichconfigured control a respective projector 201 to project images based onthe received projection data.

As present implementations are specifically directed to controlling acommon image frame, projected by both projectors 201 into blend zone205, control device 210-C can further store data related to a geometryof projectors 201; for example, in some implementations, control device210-C can store data indicative of which portion of respective images tobe projected by each projector 201 comprises a common image to beprojected into a blend zone. Such data can further be respectivelyprovided to control devices 210-A, 210-B with respective projectiondata, and each control device 210-A, 210-B can, in turn process therespective projection data into bitplanes, including masking and/orsynchronizing projected bitplanes in areas of respective projection datain the blend zone. In some implementations, such data can be stored asbitplane usage coefficients; furthermore, a bitplane mask and/orblending mask for each projector 201 can be generated therefrom.

However, in other implementations, control device 210-C can providerespective projection data to each control device 210-A, 210-B thatalready includes masking and/or synchronizing projected bitplanes inareas of respective projection data in the blend zone.

Interfaces 224 comprise any suitable wired or wireless communicationinterfaces which enable control devices 210 to communicate with eachother via a respective communication link.

Attention is now directed to FIG. 3 which depicts a flowchart of amethod 300 for reducing blend artifacts in a multiple digital projectorsystem, according to non-limiting implementations. In order to assist inthe explanation of method 300, it will be assumed that method 300 isperformed using system 200, and specifically by control devices 210, forexample when each control device 210 processes a respective application223. Indeed, method 300 is one way in which system 200 and/or controldevices 210 can be configured. Furthermore, the following discussion ofmethod 300 will lead to a further understanding of control devices 210,and system 200 and its various components. However, it is to beunderstood that system 200 and/control devices 210 and/or method 300 canbe varied, and need not work exactly as discussed herein in conjunctionwith each other, and that such variations are within the scope ofpresent implementations.

Regardless, it is to be emphasized, that method 300 need not beperformed in the exact sequence as shown, unless otherwise indicated;and likewise various blocks may be performed in parallel rather than insequence; hence the elements of method 300 are referred to herein as“blocks” rather than “steps”. It is also to be understood, however, thatmethod 300 can be implemented on variations of system 200 as well.

At block 301, control devices 210, for a given pixel of a common imageframe projected by both first projector 201-A and second projector 201-Bin blend zone 205, the given pixel of the common image frame comprisinga plurality of bitplanes arranged in a sequence, control the firstprojector 201-A to project a first portion of the plurality of bitplanesaccording to the sequence.

At block 303, control devices 210 (also for the given pixel of thecommon image frame projected by both first projector 201-A and secondprojector 201-B in blend zone 205) control the second projector 201-B toproject a second portion of the plurality of bitplanes according to thesequence, the second portion complementary to the first portion, suchthat in the common image frame only one of the first projector 201-A andsecond projector 201-B projects any given bitplane of the plurality ofbitplanes.

Method 300 will now be explained with reference to FIG. 4, which issimilar to FIG. 1, however it assumed that respective images areprojected by each projector 201-A, 201-B into respective projectionfields 203-A, 201-B onto the surface with the respective imagesoverlapping in blend zone 205. Furthermore, it is assumed that in blendzone 205, each projector 201 is projecting the same image. Put anotherway, it is assumed that for each pixel in blend zone 205, each projector201 is projecting the same respective common image frame.

It is furthermore assumed that in FIG. 4 that the brightness provided byprojector 201-A decreases linearly (e.g. from left-to-right with respectto FIG. 4) across blend zone 205, and the brightness provided byprojector 201-B increases linearly, (e.g. from left-to-right withrespect to FIG. 4) across blend zone 205. Hence, for pixels in areas ofprojection field 203-A that are outside blend zone 205, projector 201-Acontributes to 100% of the brightness, while projector 201-B contributes0% of the brightness (as projector 201-B does not project intoprojection field 201-A other than in blend zone 205).

However, from left-to-right, as depicted, about 30% of the way intoblend zone 205, projector 201-A contributes 70% of the brightness of apixel, while projector 201-B contributes the other 30% of the brightnessof the pixel; similarly, about 50% of the way into blend zone 205,projector 201-A contributes 50% of the brightness of a pixel, whileprojector 201-B contributes the other 50% of the brightness of thepixel; and about 70% of the way into blend zone 205, projector 201-Acontributes 30% of the brightness of a pixel, while projector 201-Bcontributes the other 70% of the brightness of the pixel.

Finally, for pixels in areas of projection field 203-B that are outsideblend zone 205, projector 201-B contributes to 100% of the brightness,while projector 201-A contributes 0% of the brightness (as projector201-A does not project into projection field 201-B other than in blendzone 205).

Furthermore, FIG. 4 shows the effect on bitplane projection at each ofthese positions. In particular, it is assumed in FIG. 4 that a givenpixel of a common image frame projected by each of projectors 201 inblend zone 205, is composed of 10 bitplanes, that are projected in asequence, bitplane 1, bitplane 2, bitplane 3, bitplane 4, bitplane 5,bitplane 6, bitplane 7, bitplane 8, bitplane 9, bitplane 10 (representedas 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 in FIG. 4). For example bitplane 1 cancomprise a bitplane representing a most significant bit, and bitplane 10can comprise a bitplane representing a least significant bit.Furthermore, while 10 bitplanes for each pixel are depicted, inpractise, each pixel can be represented by “B” bitplanes (in thisinstance “B” is meant to indicate an integer number of bitplanes and notan identifier of a projector and/or a projection field), which could be2^(n) bitplanes, where “n” is an integer.

In any event, with reference to the 70/30 region of blend zone 205(projector 201-A providing 70% of the brightness, and projector 201-Bprovides the remaining 30% of the brightness), projector 201-A iscontrolled to project 70% (or 7) of the bitplanes in the sequence of thecommon image frame, and projector 201-B is controlled to project 30% (or3) of the bitplanes in the sequence of the common image frame. Inparticular, the bitplanes projected by projector 201-B are complementaryto the bitplanes projected by projector 201-A. Hence, for example,projector 201-A projects bitplane 1, bitplane 2, bitplane 4, bitplane 5,bitplane 7, bitplane 8, and bitplane 10 in the sequence; while projector201-B projects complementary bitplane 3, bitplane 6, and bitplane 9 inthe sequence.

In other words, projector 201-A is controlled to project a first portionof the bitplane sequence of the common image frame, and projector 201-Bis controlled to project a second portion of the bitplane sequence ofthe common image frame, the second portion being complementary to thefirst portion. The result is that, in the common image frame, only oneof first projector 201-A and second projector 201-B projects any givenbitplane of the plurality of bitplanes of the sequence, and further onlyone projector 201 is projecting a bitplane for a given pixel at anygiven time.

Hence, there can be reduced and/or eliminated banding in blend zone 205,as compared to FIG. 1. In other words, the regions of high brightnessand low brightness have been reduced and/or eliminated, and the totalbrightness is uniform across the frame period; for example, compare thetotal “A+B” brightness of this region in FIG. 4 and FIG. 1.

Similarly, in the 50/50 region of blend zone 205 (projector 201-Aproviding 50% of the brightness, and projector 201-B provides theremaining 50% of the brightness), projector 201-A is controlled toproject 50% (or 5) of the bitplanes in the sequence of the common imageframe, and projector 201-B is controlled to project 50% (or 5) of thebitplanes in the sequence of the common image frame. In particular, thebitplanes projected by projector 201-B are complementary to thebitplanes projected by projector 201-A. Hence, for example, projector201-A projects bitplane 1, bitplane 2, bitplane 5, bitplane 8, andbitplane 10 in the sequence; while projector 201-B projects bitplane 3,bitplane 4, bitplane 6, bitplane 7, and bitplane 9 in the sequence inthe sequence. Again, compared to FIG. 1, banding is reduced and/oreliminated, and the total brightness is uniform across the frame period.

Finally, the 30/70 region of blend zone 205 (projector 201-A providing30% of the brightness, and projector 201-B provides the remaining 70% ofthe brightness), is similar to the 70/30 region, but with the projectionof respective bitplanes by each projector 201 being reversed.

It is further appreciated that the sequence can include, but is notlimited to bitplanes that have been reordered to a scheme not basedsolely on intensity. In other words, bitplanes of the sequences depictedin FIG. 4 can be reordered relative to an original sequence, and furthersome of the bitplanes of the original sequence can be turned off and/ornot form part of the sequences depicted in FIG. 4. In particular, insome situations, where certain higher intensities are to be achieved,some bit planes used for lower intensities can be turned off.

In some implementations, control device 210-C transmits respectiveprojection data to each of control devices 210-A, 210-B that has alreadybeen adapted to control each projector 201 according to method 300. Forexample, data indicative of a geometry of projectors 201 can be storedat memory 222-C, that enables control device 210-C to adapt respectiveprojection data that controls each projector 201 to project according tocomplementary bitplanes for common image frames in blend zone 205.

However, in other implementations, control device 210-C transmits, tofirst control device 210-A and second control device 210-B, the commonimage frame and associated data indicating a respective geometry of eachof first projector 201-1 and second projector 201-2 with respect toblend zone 205. As described above, data transmitted to first controldevice 210-A and second control device 210-B can be respective to eachassociated projector 201. In these implementations, each of firstcontrol device 210-A and second control device 210-B is configured tocontrol a respective projector 201 to project a respective portion ofthe plurality of the bitplanes according to the respective geometry,such that in the common image frame only one of the first projector201-A and the second projector 201-B projects any given bitplane of theplurality of bitplanes.

For example, a given combination of control device 210 and projector 201can receive data indicative of which portion of an image is to beprojected in blend zone 205 and further indicative of how manyprojectors are projecting into blend zone 205. In some implementations,such data can be represented by biplane coefficients (and/or blendcoefficients) for each pixel of blend zone 205 in the form of a bitplanemask table, and the like.

Such data can also indicate a blending scheme, such as whether theblending is to occur linearly or according to another function, and whatportion of the brightness is to be provided by a given projector 201.

Then, each combination of control device 210 and projector 201 masks(e.g. does not project) bitplanes that that are to be projected byanother projector 201, even though such masked bitplanes are present atthe control device 210. Put another way, one or more control devices 210can be configured to control each of first projector 201-A and secondprojector 201-B to interleave the first portion and the second portionof the plurality of bitplanes according to the sequence.

Indeed, in FIG. 4, one such scheme for projecting bitplanes is shown.However, other schemes are within the scope of present implementations.For example, in some alternative implementations, such projecting ofbitplanes can simply comprise projector 201-A projecting all of thefirst portion of bitplanes sequentially and, after all of the firstportion of the bitplanes are projected by projector 201-A, projector201-B projects all of the second portion of bitplanes sequentially. Inyet other alternative implementations, projectors 201 can be controlledto alternate projecting respective bitplanes. In yet furtherimplementations, a bitplanes can be allocated between projectors 201 ina common image frame according to a round-robin, which generallymaximizes how respective light output of each projector 201 is spreadout over time.

In any event, any sequence of bitplanes projected by projectors 201 in acommon image frame is within the scope of present implementations aslong as only one of first projector 201-A and second projector 201-Bprojects any given bitplane of the plurality of bitplanes in a sequencein a common image frame.

Furthermore, while method 300 is directed to a blending scheme appliedto one pixel in blend zone 205, it is assumed that method 300 is appliedto all the pixels in blend zone 205, a respective number of bitplanesprojected in a given sequence by each projector 201 depends on arespective position of a pixel.

Hence, one or more control devices 210 is further configured to: foreach of all pixels of respective common image frames projected by bothfirst projector 201-A and second projector 201-B in blend zone 205 (allthe pixels including the given pixel referred to in method 300), each ofthe pixels of the respective common image frames comprising a pluralityof respective bitplanes arranged in a respective sequence: control firstprojector 201-A to project a respective first portion of the pluralityof respective bitplanes according to the respective sequence; andcontrol second projector 201-B to project a respective second portion ofthe plurality of respective bitplanes according to the respectivesequence, the respective second portion complementary to the respectivefirst portion, such that for each of the pixels in the respective commonimage frames only one of first projector 201-A and second projector201-B projects any given respective bitplane of the plurality ofrespective bitplanes.

In some present implementations, method 300 can lead to brightness stepsin blend zone, and when projections fields 203 do not exactly overlap(e.g. a physical registration between projectors 201 is incorrect and/ornot exact), some degree of banding could still occur, though for muchsmaller time periods than the scheme of FIG. 1. Hence, in someimplementations, blend smoothness between pixels in blend zone 205 canbe addressed using dithering.

For example, in these implementations, when a target pixel intensity isno longer changed across a blend (as in FIG. 1), but bitplanes areallocated between projectors 201, as with method 300, larger steps inbrightness can occur. For example, if the load time of a bitplane is 80μsec, for a 1-chip projector with a 3000 μsec color hold time, each stepwhen shifting which of projector 201 is displaying amost-significant-bit (MSB) bitplane will shift about 2.6% (e.g. about˜80/3000×100%) of the light from one projector 201 to another projector201. If physical registration between projector images is incorrect,this could be visible, however dithering could be used to reduce thiseffect—in effect, transferring the brightness of “F” number of framesout of “D” number of frames such that the brightness shift is reduced toF/D of the bit plane step. In some instances, this could lead tosynchronization of dither between projectors and/or to use of a spatialnoise mask to manage dither across blend zone 205.

Attention is next directed to FIG. 5 which depicts a scheme 500 forimplementing method 300 at system 200 and in particular depicts bothphysical and logical components that that can be integrated into system200. Furthermore, scheme 500 takes into account dithering betweenbitplanes of adjacent pixels in blend zone 205 to increase blendsmoothness. In other words, in some implementations, one or more controldevices 210 can be further configured to dither bitplanes in adjacentpixels in blend zone 205, for each of first projector 201-A and secondprojector 201-A.

Furthermore, portions of scheme 500 can be implemented at system controldevice 210-C, while other portions can be implemented at a combinationof a control device 210-A, 210B, and a respective projector 201-A,201-B.

For example control device 210-C can process an image at a pixelintensity module 501 to determine pixel intensity of each pixel of theimage that is to be projected (e.g. using an (x,y) coordinate systemacross the image). The pixel intensities are provided to a bit planegenerator (BPG) 503, located, for example at a control device 210-A,210-B, which can convert the pixel intensities into respective“B”<=2^(n) bitplanes (rather than 10 bitplanes depicted in FIG. 4).

A blend coefficient module 505 at control device 210-C can produce amask index K (K being a counter for pixels across blend zone 205) thatis representative of the geometry between projectors 201, and for eachof 2^(n) bitplanes; bitplane coefficient module 505 can also producedithering data for dithering between 2^(m)-number of frames F, which isconditionally combined with the mask index, depending on whether maskindex K is less than 2^(n)−1 and whether a frame count, as determinedfrom a logical component 507, is greater than F, as determined at alogical component 509. If true, bitplane mask K+1 is selected from table513, thus the bitplane mask is dithered between mask K and mask K+1: forF frames out of 2^(m) frames (e.g. “D” number of frames referred toabove), the bitplane mask K+1 is used whereas in the remaining framesbitplane mask K is used. The dithering is used to smooth brightnesssteps between pixels in blend zone 205.

Bitplane mask table 513 output is combined with the respective 2^(n)bitplanes at a logical component 515 to mask the appropriate bitplanesfor the blend coefficient, which produces data that enables a bitplanemanager 517 to control a DMD 519 at a projector 201 (or other digitallycontrollable light modulator).

Persons skilled in the art will appreciate that there are yet morealternative implementations and modifications possible. For example,while implementations showing only two projectors and one blend zone arediscussed, method 300 can be extended to systems with more than twoprojectors and/or more than one blend zone including, but not limitedto, blend zones where projection fields from three or more projectorsoverlap. In these instances, the mask index K, for each projector wouldbe adapted according to the geometry of the projectors such thatblending of images from the three or more projectors in a respectiveblend zone are encoded in the mask index; such instances can includeother blend zones where projection fields from two of the three or moreprojectors overlap, similar to that described above.

Hence, the present specification is directed to “canvases” (e.g. tiledimages) created by overlapping multiple projected images projected, forexample, by multiple DLP™ projectors, and addresses a problem of aviewer perceiving blend zones, where DLP™ projected images overlap dueto banding as described with reference to FIG. 1.

The problem is generally addressed by methods described herein, whichcan include synchronization of images from the DLP™ projectors at thebitplane level, and allocation of bitplanes to each DLP™ projectorwithin a blend zone such that at most one projector produces lightduring each bitplane period.

Indeed, in such synchronization, system 200 can be frame locked, howeversystem 200 can also be bitplane locked as well, which means a commonduty cycle and hold time across all projectors 201. Without bitplanelocking, artifacts can still be reduced, but not necessarily aseffectively as described with respect to FIG. 4 (though still moreeffective than the scheme of FIG. 1).

Bitplane allocation generally occurs as described herein so that, atmost one projector is illuminating a bitplane, regardless of blend zone,including where more than two projectors overlap, for example in systemsthat comprise more than two projectors. Hence, a blend coefficientgenerator (e.g. blend coefficient module 505) can be generallyconfigured with a physical system configuration (e.g. which projectorshave adjacent and/or overlapping projection fields) and can henceallocate complementary bitplanes to each. In some implementations, thiscan be achieved using a blend projector identifier, which, for fourprojectors, can be nine values: ½, 2/2, ⅓, ⅔, 3/3, ¼, 2/4, ¾, 4/4. Theidentifier indicates which portion of a plurality of bitplanes are to beprojected by a given projector of the four projectors. For example, ablend projector identifier of x/4 indicates a blend where images from 4projectors overlap, so the bitplanes are divided into four portions, anda blend projector identifier of ¼ indicates that the given projectorshould project only the first portion, a blend projector identifier of2/4 indicates that the given projector should project only the secondportion, etc. The blend coefficient in these implementations could thenindicate the allocation of bitplanes to each projector.

In other words, method 300 can be extended to a plurality of projectors(e.g. more than two projectors); for example, system 200 can furthercomprise a plurality of projectors, including first projector 201-A andsecond projector 201-B, each having a respective projection field whichat least partially overlap in a blend zone, a given pixel of a commonimage frame projected by each of the plurality of projectors in theblend zone, the given pixel of the common image frame comprising theplurality of bitplanes arranged in a sequence, the one or more controldevices 210 (which can include control devices at each of the pluralityof projectors) being further configured to: control each of theplurality of projectors to project a respective portion of the pluralityof bitplanes according to the sequence, each of the respective portionsbeing complementary to all others of the respective portions, such thatin the common image frame only one of the plurality of projectorsprojects any given bitplane of the plurality of bitplanes. One or moreblend projector identifiers can be transmitted to each of the pluralityof projectors to indicate portions of an image being projected by agiven projector that overlap in a blend zone. Indeed, the one or moreblend projector identifiers transmitted to each of the plurality ofprojectors can be respective to a given projector to identify arespective geometry thereof. Furthermore, such a system can comprisemore than one blend zone; for example, in the four projector systemdescribed above, there can be a plurality of blend zones in whichprojection fields of pairs of the plurality of projectors overlap, indifferent combinations, another plurality of blend zones in whichprojection fields of three of the four of projectors overlap, indifferent combinations, and a blend zone in which projection fields ofall four of projectors overlap (however, when a surface and/or a screen,and the like, onto which images are projected is not flat there could bea plurality of blend zones in which projection fields of all four ofprojectors overlap).

In yet further implementations, control device 210-C can transmitassociated data indicating a respective geometry to each of controldevices 210-A, 210-B and associated projectors 201 (and/or each of aplurality of projectors and associated control devices), for exampleduring a setup process, and then control device 210-C can bedisconnected from other components in system 200. In other words,control device 210-C need not be in continuous communication withprojectors of system 200, and only in communication during the setupprocess. Projectors 210 of system 200 (and/or associated control devices210 (other than control device 210-C)) can then proceed to divvy up thebit planes according to method 300 and/or according to a respectiveapplication 223. In other words, geometry data (such as blend projectoridentifiers) can be stored at each projector and need not becontinuously updated from an image generator (such as control device210-C and the like).

Furthermore, as content can be distributed from control device 210-C tothe projectors and/or to the other control devices, whether controldevice 210-C is in continuous or non-continuous communication therewith,system 200 can comprise a content distribution system. Hence, method 300can comprise a method implemented in content distribution systemcomprising two or more projectors and one or more control devices.

It is yet further appreciated that techniques described herein can beused in other applications, for example at a pulsed width modulation(PWM) type image modulator; in other words, PWM duty cycles could bemanaged using method 300 presuming a sufficient number of “bitplanes” isused to cover time slices created by the smallest allowed change in PWMduty cycle.

In any event, provided herein is a system and method reducing blendartifacts in a multiple digital projector system. In particular,projectors in the system are coordinated such that bitplanes in blendzones are projected by one projector at one time, the bitplanes of apixel distributed between the projectors such that only projector isprojecting a given bitplane of a given pixel at any given time.

Those skilled in the art will appreciate that in some implementations,the functionality of control devices 210 can be implemented usingpre-programmed hardware or firmware elements (e.g., application specificintegrated circuits (ASICs), electrically erasable programmableread-only memories (EEPROMs), etc.), or other related components. Inother implementations, the functionality of control devices 210 can beachieved using a computing apparatus that has access to a code memory(not shown) which stores computer-readable program code for operation ofthe computing apparatus. The computer-readable program code could bestored on a computer readable storage medium which is fixed, tangibleand readable directly by these components, (e.g., removable diskette,CD-ROM, ROM, fixed disk, USB drive). Furthermore, it is appreciated thatthe computer-readable program can be stored as a computer programproduct comprising a computer usable medium. Further, a persistentstorage device can comprise the computer readable program code. It isyet further appreciated that the computer-readable program code and/orcomputer usable medium can comprise a non-transitory computer-readableprogram code and/or non-transitory computer usable medium.Alternatively, the computer-readable program code could be storedremotely but transmittable to these components via a modem or otherinterface device connected to a network (including, without limitation,the Internet) over a transmission medium. The transmission medium can beeither a non-mobile medium (e.g., optical and/or digital and/or analogcommunications lines) or a mobile medium (e.g., microwave, infrared,free-space optical or other transmission schemes) or a combinationthereof.

Persons skilled in the art will appreciate that there are yet morealternative implementations and modifications possible, and that theabove examples are only illustrations of one or more implementations.The scope, therefore, is only to be limited by the claims appendedhereto.

What is claimed is:
 1. A system comprising: a first projector having afirst projection field and a second projector having a second projectionfield, the first projection field and the second projection fieldoverlapping in a blend zone, each of the first projector and the secondprojector comprising a respective digital projector configured to:digitally project images where each projector pixel is either on or offat any given time; and control brightness of pixels in projected imagesusing bitplanes; and one or more control devices configured to: for agiven pixel of a common image frame projected by both the firstprojector and the second projector in the blend zone, the given pixel ofthe common image frame provided by a plurality of bitplanes eachrepresenting a different significant bit of pixel intensity of the givenpixel, the plurality of bitplanes arranged in a sequence, control thefirst projector to project a first portion of the plurality of bitplanesin the sequence; and control the second projector to project a secondportion of the plurality of bitplanes in the sequence, the secondportion complementary to the first portion, only one of the firstprojector and the second projector projecting any given bitplane in thesequence in the common image frame at any given time, the sequence beingotherwise common to the first projector and the second projector in theblend zone, a first number of the bitplanes in the first portion, and asecond number of the bitplanes in the second portion, each beingdependent on a position of the given pixel in the blend zone, the firstnumber being larger than the second number when the position is towardsthe first projection field, with respect to a center of the blend zone,and the second number being larger than the first number when theposition is towards the second projection field, with respect to thecenter of the blend zone, wherein a portion of an image to be projectedin the blend zone and a number of projectors are projecting into theblend zone is represented by blend coefficients for pixels across theblend zone in a form of a bitplane mask table, the one or more controldevices are further configured to dither brightness of frames in theblend zone by: converting pixel intensities of the pixels in the imageinto the plurality of bitplanes, a number of the plurality of bitplanesbeing 2^(n), where “n” is an integer; producing a mask index K, where Kis a counter for the pixels across the blend zone, the mask index Krepresentative of geometry between the first projector and the secondprojector and each of the 2^(n) bitplanes; producing dithering data fordithering between an F number of frames; when the mask index K is lessthan 2^(n)−1 and when a frame count is greater than the F number offrames, select a bitplane mask K+1 from the bitplane mask table andotherwise select a bitplane mask K, to dither between the bitplane maskK and the bitplane mask K+1; and combining a selected bitplane mask witha respective bitplane of the plurality of bitplanes to control arespective light modulator at the first projector and the secondprojector.
 2. The system of claim 1, wherein the one or more controldevices comprises a first control device at the first projector, asecond control device at the second projector, and one or more systemcontrol devices in communication with the first control device and thesecond control device, the one or more system control devices configuredto: transmit, to the first control device and the second control device,the common image frame and associated data indicating a respectivegeometry of each of the first projector and the second projector withrespect to the blend zone, each of the first control device and thesecond control device configured to control a respective projector toproject a respective portion of the plurality of the bitplanes accordingto the respective geometry.
 3. The system of claim 1, wherein each ofthe first projector and the second projector are controlled to project arespective portion of the plurality of bitplanes in the sequenceaccording to a blend coefficient determined from associated dataindicating a respective geometry of each of the first projector and thesecond projector with respect to the blend zone.
 4. The system of claim1, wherein the one or more control devices are further configured to:for each of all pixels of the common image frame projected by both thefirst projector and the second projector in the blend zone, all thepixels including the given pixel, each of the pixels of the common imageframe comprising a plurality of respective bitplanes arranged in arespective sequence: control the first projector to project a respectivefirst portion of the plurality of respective bitplanes according to therespective sequence; and control the second projector to project arespective second portion of the plurality of respective bitplanesaccording to the respective sequence, the respective second portioncomplementary to the respective first portion, and for each of thepixels in the common image frame only one of the first projector and thesecond projector projects any given respective bitplane in therespective sequence.
 5. The system of claim 1, wherein the one or morecontrol devices are further configured to control each of the firstprojector and the second projector to interleave the first portion andthe second portion of the plurality of bitplanes in the sequence.
 6. Thesystem of claim 1, wherein the one or more control devices are furtherconfigured to dither adjacent bitplanes for each of the first projectorand the second projector in the blend zone.
 7. The system of claim 1,wherein each of the first projector and the second projector compriseone or more of a a DMD (digital multimirror projector) based projectorand an LCOS (liquid crystal on silicon) projector operated in an on-offmode.
 8. The system of claim 1, wherein each of the first projector andthe second projector is configured to mask respective bitplanes in thesequence that are not to be respectively projected.
 9. The system ofclaim 1, wherein each of the first projector and the second projectorare controlled to project a respective portion of the plurality ofbitplanes in the sequence according to a round-robin.
 10. The system ofclaim 1, further comprising a plurality of projectors, including thefirst projector and the second projector, each having a respectiveprojection field which at least partially overlap in the blend zone, thegiven pixel of the common image frame projected by each of the pluralityof projectors in the blend zone, the given pixel of the common imageframe comprising the plurality of bitplanes arranged in the sequence,the one or more control devices are further configured to: control eachof the plurality of projectors to project a respective portion of theplurality of bitplanes according to the sequence, each of the respectiveportions being complementary to all others of the respective portions,only one of the plurality of projectors projecting any given bitplane inthe sequence in the common image frame at any given time.
 11. A methodcomprising: at a system comprising: a first projector having a firstprojection field and a second projector having a second projectionfield, the first projection field and the second projection fieldoverlapping in a blend zone, each of the first projector and the secondprojector comprising a respective digital projector configured to:digitally project images where each projector pixel is either on or offat any given time; and control brightness of pixels in projected imagesusing bitplanes; and one or more control devices, for a given pixel of acommon image frame projected by both the first projector and the secondprojector in the blend zone, the given pixel of the common image frameprovided by a plurality of bitplanes each representing a differentsignificant bit of pixel intensity of the given pixel, the plurality ofbitplanes arranged in a sequence, controlling, using the one or morecontrol devices, the first projector to project a first portion of theplurality of bitplanes in the sequence; and controlling, using the oneor more control devices, the second projector to project a secondportion of the plurality of bitplanes in the sequence, the secondportion complementary to the first portion, only one of the firstprojector and the second projector projecting any given bitplane in thesequence in the common image frame at any given time, the sequence beingotherwise common to the first projector and the second projector in theblend zone, a first number of the bitplanes in the first portion, and asecond number of the bitplanes in the second portion, each beingdependent on a position of the given pixel in the blend zone, the firstnumber being larger than the second number when the position is towardsthe first projection field, with respect to a center of the blend zone,and the second number being larger than the first number when theposition is towards the second projection field, with respect to thecenter of the blend zone, wherein a portion of an image to be projectedin the blend zone and a number of projectors are projecting into theblend zone is represented by blend coefficients for pixels across theblend zone in a form of a bitplane mask table, wherein the methodfurther comprises dithering brightness of frames in the blend zone by:converting pixel intensities of the pixels in the image into theplurality of bitplanes, a number of the plurality of bitplanes being2^(n), where “n” is an integer; producing a mask index K, where K is acounter for the pixels across the blend zone, the mask index Krepresentative of geometry between the first projector and the secondprojector and each of the 2^(n) bitplanes; producing dithering data fordithering between an F number of frames; when the mask index K is lessthan 2^(n)−1 and when a frame count is greater than the F number offrames, select a bitplane mask K+1 from the bitplane mask table andotherwise select a bitplane mask K, to dither between the bitplane maskK and the bitplane mask K+1; and combining a selected bitplane mask witha respective bitplane of the plurality of bitplanes to control arespective light modulator at the first projector and the secondprojector.
 12. The method of claim 11, wherein the one or more controldevices comprises a first control device at the first projector, asecond control device at the second projector, and one or more systemcontrol devices in communication with the first control device and thesecond control device, the method further comprising: transmitting,using the one or more system control devices, to the first controldevice and the second control device, the common image frame andassociated data indicating a respective geometry of each of the firstprojector and the second projector with respect to the blend zone, eachof the first control device and the second control device configured tocontrol a respective projector to project a respective portion of theplurality of the bitplanes according to the respective geometry.
 13. Themethod of claim 11, wherein each of the first projector and the secondprojector are controlled to project a respective portion of theplurality of bitplanes in the sequence according to a blend coefficientdetermined from associated data indicating a respective geometry of eachof the first projector and the second projector with respect to theblend zone.
 14. The method of claim 11, further comprising: for each ofall pixels of the common image frame projected by both the firstprojector and the second projector in the blend zone, all the pixelsincluding the given pixel, each of the pixels of the common image framecomprising a plurality of respective bitplanes arranged in a respectivesequence: controlling, using the one or more control devices, the firstprojector to project a respective first portion of the plurality ofrespective bitplanes according to the respective sequence; andcontrolling, using the one or more control devices, the second projectorto project a respective second portion of the plurality of respectivebitplanes according to the respective sequence, the respective secondportion complementary to the respective first portion, and for each ofthe pixels in the common image frame only one of the first projector andthe second projector projects any given respective bitplane in therespective sequence.
 15. The method of claim 11, further comprisingcontrolling, using the one or more control devices, each of the firstprojector and the second projector to interleave the first portion andthe second portion of the plurality of bitplanes in the sequence. 16.The method of claim 11, further comprising dithering, using the one ormore control devices, adjacent bitplanes for each of the first projectorand the second projector in the blend zone.
 17. The method of claim 11,wherein each of the first projector and the second projector isconfigured to mask respective bitplanes in the sequence that are not tobe respectively projected.
 18. The method of claim 11, wherein each ofthe first projector and the second projector are controlled to project arespective portion of the plurality of bitplanes in the sequenceaccording to a round-robin.
 19. The method of claim 11, wherein thesystem further comprises a plurality of projectors, including the firstprojector and the second projector, each having a respective projectionfield which at least partially overlap in the blend zone, the givenpixel of the common image frame projected by each of the plurality ofprojectors in the blend zone, the given pixel of the common image framecomprising the plurality of bitplanes arranged in the sequence, themethod further comprising: controlling, using the one or more controldevices, each of the plurality of projectors to project a respectiveportion of the plurality of bitplanes according to the sequence, each ofthe respective portions being complementary to all others of therespective portions, only one of the plurality of projectors projectingany given bitplane in the sequence in the common image frame at anygiven time.
 20. A non-transitory computer-readable medium storing acomputer program, wherein execution of the computer program is for: at asystem comprising: a first projector having a first projection field anda second projector having a second projection field, the firstprojection field and the second projection field overlapping in a blendzone, each of the first projector and the second projector comprising arespective digital projector configured to: digitally project imageswhere each projector pixel is either on or off at any given time; andcontrol brightness of pixels in projected images using bitplanes; andone or more control devices, for a given pixel of a common image frameprojected by both the first projector and the second projector in theblend zone, the given pixel of the common image frame provided by aplurality of bitplanes each representing a different significant bit ofpixel intensity of the given pixel, the plurality of bitplanes arrangedin a sequence, controlling, using the one or more control devices, thefirst projector to project a first portion of the plurality of bitplanesin the sequence; and controlling, using the one or more control devices,the second projector to project a second portion of the plurality ofbitplanes in the sequence, the second portion complementary to the firstportion, only one of the first projector and the second projectorprojecting any given bitplane in the sequence in the common image frameat any given time, the sequence being otherwise common to the firstprojector and the second projector in the blend zone, a first number ofthe bitplanes in the first portion, and a second number of the bitplanesin the second portion, each being dependent on a position of the givenpixel in the blend zone, the first number being larger than the secondnumber when the position is towards the first projection field, withrespect to a center of the blend zone, and the second number beinglarger than the first number when the position is towards the secondprojection field, with respect to the center of the blend zone, whereina portion of an image to be projected in the blend zone and a number ofprojectors are projecting into the blend zone is represented by blendcoefficients for pixels across the blend zone in a form of a bitplanemask table, and wherein execution of the computer program is for furtherdithering brightness of frames in the blend zone by: converting pixelintensities of the pixels in the image into the plurality of bitplanes,a number of the plurality of bitplanes being 2^(n), where “n” is aninteger; producing a mask index K, where K is a counter for the pixelsacross the blend zone, the mask index K representative of geometrybetween the first projector and the second projector and each of the2^(n) bitplanes; producing dithering data for dithering between an Fnumber of frames; when the mask index K is less than 2^(n)−1 and when aframe count is greater than the F number of frames, select a bitplanemask K+1 from the bitplane mask table and otherwise select a bitplanemask K, to dither between the bitplane mask K and the bitplane mask K+1;and combining a selected bitplane mask with a respective bitplane of theplurality of bitplanes to control a respective light modulator at thefirst projector and the second projector.